1.) Doesn't matter. It should just get the reader interested.
2.) Usually 10 chapters. Each chapter has 19 pages, which makes around 200 pages with extra stuff. That's for weekly manga. It depends on the release schedule.
4.) Nope. There are many manga out there, which don't have great drawings, but are still successful and vice versa. Nice drawings don't equal success.
Just work hard and do your best! Also, your first manga will probably not be good. Masashi Kishimoto (Naruto) and Tite Kubo (Bleach) both published manga that weren't good before their big hits.